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Cold frame night temperature

using spray foam sealant

It was 5 degrees warmer inside our new cold frame than the outside temp.

Adding some silicone and spray foam sealant today should help to keep it even warmer tonight.



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Normally hea-reflacting films are applied to glass to keep infrared radiation outside the house. But what if you'd apply it to the other side of the glass to keep infrared radiation in? (Not sure if this would work; I haven't seen the most recent films in action)

Another approach might be to put a blanket of fiberglass or stone wool insulation on top of the cold frame windows at night. But this is of course an extra to-do item twice a day.

Comment by Roland_Smith Tue Mar 17 16:52:39 2015

I've been keeping track of the temps in my cold frame as well, but mine is not attached like yours to the house. It sits outside in one of the raised beds that have concrete around the edges and has two one-gallon glass containers filled with water and black paint. On March 8th the low was 30 degrees in it, but the last week the low has been 40. Just perfect for hardening off my brassicas and lettuce, which I am now transferring to the raised beds.

Maybe painting the concrete black would assist with heat retention?

Comment by Na Yan Tue Mar 17 18:53:01 2015

I am a big fan of cold frames. We had several on the south side of our house in the mountains, and even with outside temps in the single digits, and a couple of times below zero, I never lost a plant to the cold. The ones closest to the edges might have some frostbite on the leaves, but everything survived. I just put a couple of jugs of water inside mine tonight, since the temps are supposed to get down to near single digits. But I suspect they will be okay. Now, forgetting to open them on a warm day and burning all the plants to a crisp, that's a different story. :-)

Comment by deb Tue Mar 17 19:05:31 2015
Instead of fiberglass insulation, just throw an old blanket or sheet over the cold frame at night if you expect really low temps. It will block most of the radiant heat transfer, and add a little insulation to prevent convective heat transfer.
Comment by Jim Tue Mar 17 21:41:02 2015
Heat loss from a cold frame once the sun goes down is not due very much to radiation out thru the glass, but due to convection (frame not airtight) & most importantly by conduction: the low density, warm air equilibrating temp with the higher density, cooler walls, glass & ground. That's why double pain glass holds in heat better than single pain. Having a heat sink like water jugs slows the cooling, but they usually aren't big enough to make a big difference.
Comment by doc Wed Mar 18 07:27:40 2015

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